The lymphokine, Macrophage Migration Inhibition Factor (MIF), has been identified as a mediator of the function of macrophages in host defence and its expression correlates with delayed hypersensitivity and cellular immunity. A 12,000 da protein with MIF activity was identified by Weiser et al, Proc. Natl. Acad. Sci. U.S.A., 86, 7522-7526 (1989). MIF was first characterized by expression cloning from activated human T-cells, however, the abundance of the product is low in these cells. No MIF protein is commercially available, although the human cDNA is marketed by R&D Systems Inc., Minneapolis, Minn.
The eye lens contains high concentrations of soluble proteins, Harding et al, The Eye, ed. Davson, H., Academic Press, New York, Vol. 1B, pp 207-492; Wistow et al, Ann. Rev. Biochem., 57, 479-504 (1988); and Histow et al, Nature, 326, 622-624 (1987).
The most abundant proteins, the crystallins, are structural, comprising the refractive material of the tissue. Some crystallins are specialized for the lens, others are identical to enzymes expressed in lower amounts in other tissues. Individual crystallins may account for a quarter or more of total lens protein, Wistow et al, Nature, 326, 622-624 (1987) and Wistow et al, PNAS, 87, 6277-6280 (1990). However, other proteins are also present at moderate abundance, typically in the range 0.1-1% of total protein. Some of these are also enzymes, such as .alpha.-enolase or aldehyde dehydrogenase, found as crystallins in some species, Wistow et al, J. Mol. Evol., 32, 262-269 (1991).